Relay nodes were introduced in Rel-10 of the 3GPP standards documentation to provide coverage extension within the cell operated by a base station (eNB), as a tool to improve, for example, the coverage of high data rates for User Equipment (UE), temporary network deployment, cell edge throughput and/or to provide coverage in new cell areas. Mobile RNs (MRNs) are also included in Rel-11 as a study item and the deployment use case is limited to high speed trains where the relay node in mounted on and moves with the train. The LTE specifications support relaying by having a Relay Node (RN) wirelessly connected to a base station (referred to as a Donor eNB (DeNB)). In addition to serving its own ‘donor’ cell, the Donor eNB serves the RN, via a modified version of the Evolved Universal Terrestrial Radio Access (E-UTRA) radio interface. The modified interface is referred to as the ‘RN-Un’ interface.
Each RN is provided with many aspects of a base station's functionality and is therefore capable of acting as a base station serving user equipment in its own ‘relay’ cell via a wireless interface referred to as the ‘RN-Uu’ interface. From the perspective of the user equipment in the relay cell, therefore, the RN essentially appears to be a conventional LTE base station. Typically a RN will be serving multiple UEs so the aggregated data for all these UEs must pass over the RN-Un interface. In addition to the base station functionality, however, the RN also supports a subset of the UE functionality including, for example, many aspects of the physical layer, layer-2, radio resource control (RRC), and non access stratum (NAS) functionality, to allow it to connect wirelessly to the Donor eNB (DeNB).
The DeNB is capable of handling communication ‘directly’ to and from user equipment camped in its own cell via a conventional ‘Uu’ interface between the DeNB and the user equipment. The DeNB is also capable of handling communication ‘indirectly’ with user equipment camped in the relay cell, via the RN-Un interface, the RN, and the RN-Uu interface.
As those skilled in the art will understand, conventional eNBs have the capability of interconnecting with one another via an interface referred to as the ‘X2’ interface. The eNBs also connect to a core network comprising an Evolved Packet Core (EPC) by means of an interface referred to as the ‘S1’ interface and, more specifically, to a Mobility Management Entity (MME) of the EPC via an ‘S1-MME’ interface and to a Serving Gateway (S-GW) by means of an ‘S1-U’ interface.
The DeNB is therefore required to provide S1 and X2 proxy functionality between the RN and other network nodes (other eNBs, MMEs and S-GWs) meaning that, depending on the context, the DeNB appears as an MME (for S1), an eNB (for X2) and an S-GW, to the RN. Thus, in addition to terminating the conventional radio protocols of the modified E-UTRA radio interface (RN-Un), the RN is also capable of terminating the protocols of the S1, S11 and X2 interfaces.
The 3GPP standards documentation defines in Section 4.7 of TS 36.300 v11.1.0 (the content of which is herein incorporated by reference) the architecture of RNs and the way in which they establish connections with the DeNB. The 3GPP standards documentation defines in Section 9 of TR 36.814 v2.0.0 (the content of which is herein incorporated by reference) different types of RN in Rel-10 which differ in the way that the RN-Un interface is provided:                1. Type 1 RNs re-use the same frequency for both the RN-Uu interface (RN-to-UE) and the RN-Un interface (RN-to-DeNB) by configuring some sub-frames for RN-Uu and some for RN-Un. This may be considered as a kind of half-duplex operation.        2. Type 1a RNs use different frequencies for RN-Uu and RN-Un.        3. Type 1b RNs also re-use the same frequency for RN-Uu and RN-Un but do so by using separate isolated antennas, so that both RN-Uu and RN-Un can operate at the same time (full-duplex operation).        
Type 1 RNs must share bandwidth between RN-Uu and RN-Un and this may result in lower throughput than can be achieved by Type 1a and Type 1b RNs. In the case of Type 1 there is also a need to configure the number of sub-frames assigned for the RN-Un interface such that the throughputs on the RN-Uu and RN-Un interfaces are balanced. Depending on the number of UEs being served by the relay node, this may affect the services that the relay node can provide to each UE.